6 Volt Marine Battery Conversion

I got into a discussion yesterday about how to convert a 2 battery, 12 volt house battery bank into a 2 battery, 6 volt battery bank utilizing golf cart style batteries. I thought that I’d share it with you here.

And the first question is, why would you want to do this?

A few years back the golf cart people discovered that they could get more run time on electric golf carts by using 6 volt batteries connected in series (which provides 12 volts) than they could by connecting 12 volt batteries in parallel. Recently boaters and RV’ers have discovered the same thing and the 6 volt battery combo has seen a recent growth in popularity.

Before we continue let’s look at a couple of the basic rules of electricity as they apply to battery configurations.

Connecting batteries in parallel (positive to positive and negative to negative) results in the voltage remaining as one battery however the capacity (amp hours) will be the sum of both batteries.

Connecting two 12 volt / 110 amp hour batteries in parallel will result in a 12 volt bank with a capacity of 220 amp hours.

Connecting batteries in series (positive in and negative to positive connecting the batteries with negative out) results in the voltage being the sum of both batteries and the capacity remaining as one battery.

Connecting two 6 volt / 220 amp hour batteries in series will result in a 12 volt bank with a capacity of 220 amp hours.

Hmmmm, what’s the difference you might ask?

Well here it is. 12 volt batteries are comprised of 6 cells and 6 volt batteries are comprised of 3 cells. What this means is that 6 volt batteries have larger cells with plates that are more robust and each cell has an increased electrolyte volume. Because of this they can easily withstand longer and deeper discharges than 12 volt batteries of equal capacity. 6 volt batteries also have a smaller footprint (7.1×10.25”) that a comparable Group 27 12volt, battery (6.75×12.75”) however 6 volt batteries are slightly taller (11.25”) as opposed to their 12 volt counterpart (9.5”). Be sure to factor in this height difference when considering this change. The sizes listed above are an aveage but they should be close.

Also, if you have the larger 4D or 8D batteries fitted, and if you refer to the battery size chart on an earlier posting, from a size and weight standpoint alone, the advantage of the 6 volt deal becomes obvious.

Here’s how you do it.

6 volt batteries wired in parallel

The above diagram shows the two 6 volt (each@220ah) batteries wired in series and connected to bank 1 of the battery master switch. A separate starting battery is connected to position 2 of the switch. This gives us 12 volts and 220 amp hours capacity.

Heres another popular combination if your serious about some extended off shore jaunts.

four 6v batteries

Do the math. On this one we have two pairs of 6 volt batteries (@220 ah) each wired in parallel  and with the pairs wired in series we have a bank that produces 12 volts and a capacity of 440 amp hours.

Fiberglass Gel Coat Restoration

A while back I was working on a boat in a local yard when I happened to strike up a conversation with a fellow that owned the boat next to the one that I was working on. I immediately noticed the shine on the hull (It was a sailboat, about 35 years old) and I asked if it had recently been painted. The answer was no but that he had just applied a product called Poliglow to the hull topsides. I have to admit that the hull was clean and the shine was impressive especially considering the boat’s age.


Here’s a picture of the hull I’m talking about.

Now I’ve seen this stuff on the shelves for years under various brand names Vertiglass, Poliglow, Vivilon to name a few and I have to admit that I have never paid much attention to them preferring instead to use the “sand and conpound method” in my attempts to restore aged gel coat. After checking out the finish on the aforementioned boat I decided that maybe this deserves more research. Off I went into cyberspace and a few hours later I was able to compile enough data to make me think that this may be a viable way to re-store and maintain the appearance of fiberglass gel coat. Especially interesting was a post on one of the sailing forums by a fellow who seems to have had considerable experience with this method and abviously knew what he was talking about. We’ll discuss that further in a bit. Next, let’s start with the basics and discuss the three most common methods of gel coat restoration and some of the pros and cons of each.

1- Sand, Compound and Wax

Abrade it down using whatever, compounds, sandpapers, scotch pads, necessary. It all does the same thing, and then slowly reduce the grit size to create a smooth finish and then keep it protected because if it goes bad again, you may not have any gel coat left to restore it.

Note: This removes Gel Coat

2-Wax, Wax and More Wax

Wax it and keep it from getting worse. This may or may not improve the oxidized appearance, depending on the original condition of the surface. Wax is not very viscous and may not be a great aesthetic solution, but you keep it from getting worse and you don’t reduce the gel coat.

3-The “Shine in a Bottle” Method

Disclaimer: Before we go any further I just want to point out that I have NOT done this myself but may in the very near future. The method that I’m about to describe has been compiled from various sources of information that I have uncovered in my search.

Seal it and restore the surface gloss and color using a thin sealer that is tough and durable. There are good ones and less than good ones. A couple of well-known brand names are Poliglow and Vertiglass. I suggest that some re-search is in order before you jump in the try this. The main argument against the above products is that, while they do provide a shiny surface and are a good aesthetic solution some are not very durable and vinyl fenders may abrade the surface.

A post on one of the forums indicated that “what you want is a high solids, metal interlocked, acrylic-copolymer designed for high durability with UV absorbers” commonly known as commercial grade floor wax and to look for a Product with 20% solids or higher.

A product that fits the bill is Zep High Traffic Floor Finish, available at any Home Depot store. It’s reasonably priced, has UV absorbers and can be easily removed, if desired with available products. It is also reported to be very durable.

Material List

-Zep High Traffic Floor finish (available at Home Depot)

-Bar Keeper’s Friend (powdered, available at most hardware stores)

-TSP (Trisodium Phosphate, powdered and available at hardware stores in the paint department)

-3M scrubbies (white, fine)

-Microfiber rags (white or laundered)

-Latex gloves
Surface Prep and Application

  • Clean the Hull. First use “Bar Keeper’s Friend” and a fine 3M scrubbie. Removes surface dirt and Gel Coat Chalk.
  • Wash the surface with “TSP” (trisodium phosphate). This removes any surface oil and silicone.
  • Use a garden sprayer and mist surface with water, examine for water beading to ensure that no silicone or oil is present.
  • Dry the surface prior to application.
  • Apply wax with a damp Microfiber cloth and “wipe” it on. Dries in minutes, is self-levelling and continue for 4-6 coats until desired gloss is achieved.

The first 1-2 coats will probably look somewhat blotchy but after you get 3-4 coats applied the surface should develop a good even shine.


Re-apply 1-2 coats each season.

Ok over decals and makes for easy dirt removal

Waking Up (charging) Dead Marine Batteries

Just in case you’ve been a little negligent in battery maintenance over the winter and your batteries won’t charge try this…… Plug the boat in and turn the battery switch to “Both” to connect both banks if you have more than one. Then turn on a passive DC appliance such as the cabin lights and put a load on the system with the charger energized. Leave it for a couple of hours and this just might kick start the battery charger. Once the charger starts you can turn the lights off and let the battery charge as you normally would.

Since a dead battery has no internal resistance and offers little or no load on the charger, loading the system in this way might just be enough to get the charger going. Most chargers need to see a small load in order to initiate.

By the way if this doesn’t work you’re going shopping.

Ethanol in Gasoline as a Marine Fuel

These past few years there has been a lot of scuttlebutt surrounding the use of Ethanol in gasoline sold for marine use. Ethanol (ethyl alcohol) is the same type of alcohol found in booze and is produced agriculturally from crops such as potatoes, sugar cane and corn. In North America it is common to find ethanol levels up to 15% in commercially available gasoline.

Ethanol has three characteristics which as boaters we need to be aware of:

  • Ethanol is more corrosive that gasoline. It can attack aluminum engine fuel system components and it can be very damaging to many types of rubber, neoprene and yes even fiberglass. Since boats, in many cases have a much longer service life than cars, a large number of boats in use today were manufactured before ethanol was even considered as a motor fuel component and as such, engines and fuel systems are susceptible to its corrosive effects. This includes carburetors, fuel injectors, fuel pumps, neoprene fuel lines and tank fill hoses, fiberglass fuel tanks and any other component that is used to convey fuel.
  • Ethanol is Hygroscopic. As we learned in a past post about fiberglass hull construction, hygroscopic means that it can absorb water. This can affect its corrosiveness and with water being a conductor of electricity can make static electricity build up at the filler neck even more of an issue.
  • Ethanol when added to gasoline severely shortens the fuel’s “shelf life”. In many areas due to the onset of winter weather boats are hauled out and dry stored for 6 months every year. In these scenarios a fuel’s shelf life becomes an important issue.

So what does this mean for us boaters? Let me start by saying that the automotive world has largely adapted to these changes and cars and trucks available today are “ethanol friendly” and are for the most part immune to the potentially damaging effects of ethanol gasoline. Also cars and trucks are generally not stored for months on end so a fuels shelf life is usually not an issue.

The next question is, as a boater how do I know if a fuel contains ethanol or not. It “should” be noted on the gas pump in plain view but be careful, it may not be and depending on the area that you’re in it may not even be required. There’s a great website that I highly recommend that you visit if you wish to re-search this further. It is www.pure-gas.org.

Now let’s suppose thatif  your boat resides in an area where it is impossible to obtain ethanol free fuel, let me offer a few tips.

  • Of course first the obvious. Try and use ethanol free fuels whenever possible. The best way to counteract the effects of ethanol is by the use of a quality fuel additive. There are many on the market and I suggest that some fairly extensive re-search is in order.
  • Since neoprene is used extensively on boats for fuel lines and fill hoses and the only types of neoprene that are ethanol resistant are USCG Type A1, A15 and A2. ABYC recommends that A1 and A15 are the only types to be used as fuel supply lines and A2 is the only type recommended as a tank fill hose I highly recommend that you replace any lines and hoses that are not of the above types.
  • If your boat is fitted with a plastic or Marelon deck fuel fill fitting I recommend that it be replaced with a metal one and that it be grounded (connected with a wire) to the remainder of the on board metallic fuel system components. This will allow you to equalize the fuel’s static electrical current build-up by touching the fill nozzle to the grounded fitting. Plastic fittings do not allow for this
  • Don’t forget about you outboard motoes and gensets.

That’s the basics for now but since this is a very hot topic I will no doubt be posting on this subject again as we move forward. Consider this: Since we have now figured out how to “grow” gasoline I would expect the levels of ethanol in fuel to increase rather than decrease.

Stay tuned!

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